What is the ruling on someone who was present (muqim) when the time for an obligatory prayer began, then traveled before performing it—does he pray it shortened (qaṣr) or in full (tamām)?

The madhhab of the majority of scholars (Hanafis, Malikis, Shafi'is, and one narration from Ahmad) is that whoever is at home when the time for prayer begins, and then travels, may shorten the prayer (qasr). This has been narrated as a consensus (ijma'). As for the relied-upon position of the Hanbali madhhab, it is to pray in full (itmam).